[U-Boot] FPGA relocation/C environment

[Graeme Russ <graeme.russ@gmail.com>]

Wolfgang Wegner wrote:
> Hi,
> 
> thank you all for all the comments so far.
> 
> It seems I have at least 2 problems:
> - my gcc (m68k-elf-gcc (Sourcery G++ Lite 4.3-208) 4.3.3) does not
>   produce correctly relocatable code; no matter if I give -fPIC or
>   not (-mrelocatable is not accepted at all), I do not get any
>   entries in .got2 or .fixup, only .got

-mreloctable only applies to PPC CPUs - not version of gcc will give you
.got2 and .fixup unless you are building for PPC

>   However, there still may be anything wrong in my conclusion,
>   because I can use this compiler to compile uClinux-dist-20071107
>   and get working applications (which, as far as I understand, have
>   to be relocated at runtime, too, but I do not know if any of these
>   use such features as statically initialized function pointers that
>   I have in the U-Boot fpga code...).

They are build and linked as pic or pie (position independent executable)
This puts information in the elf binary that the dynamic loader/linker
can user to modify the executable as it is loaded into memory to enable
it to run at the target load address

> - the current coldfire startup code (at least for MCF532x/MCF537x)
>   would not handle these sections even if they existed - however,
>   this seems to be rather easily (i.e. maybe even I could do it)
>   fixed, looking at the ppc examples.

You might want to look at the x86 example instead. I posted a patch a
while ago (http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/68923)

> 
> I will first live with the problem (relocating the fpga struct pointers
> in my own board code, where it is filled anyways - for coldfire,
> gd->reloc_off is still present) and see if I can get hold of a better
> gcc version.

Yes, this manual 'fixup' will work, but the long term goal is to remove
this

> I tried gcc-4.4.1, but was unable to compile one of U-Boot or uClinux,
> so switched back to this one which I found to compile (old and current)
> U-Boot, old uClinux _and_ support mcf5445x, which I am designing in
> now...
> 
> Thank you and sorry for my stupid questions.

Not stupid at all - Proper relocation can be very tricky to achieve. I
spent a _long_ time getting it to work for x86, and in the end the
solution is rather trivial - Have a search through the u-boot mailing
list ;)

> 
> Regards,
> Wolfgang
> 

Regards,

Graeme